Prior art input architectures for a linear circuit ordinarily comprise a resistor voltage divider network to transform the voltage to a level upon which the circuit can operate. Supply power is corrected and controlled through the use of the power factor controller such as shown in prior art FIG. 1. The value of line voltage is reduced to a level which will not damage the integrated circuit IC through a resistor voltage divider network. In the circuit of FIG. 1, the rectified line voltage of 127 to 380 volts peak is coupled to the IC through the resistor divider network which comprises a 650K ohms resistor R1 connected between the rectified line voltage and to the input pin and a 2K ohm resistor R2 connected between the input pin and the system ground 10. The input signal to the IC is a voltage. The input circuit in the IC is a circuit for receiving a voltage signal. A voltage buffer 18 is coupled to the IC input pin 12 to receive the voltage signal. The buffer 18 is in series with a current limiting resistor 20. The resistor 20 is also coupled to the anode of a diode D1 and to the base of a bipolar NPN transistor T1. The diode D1 is coupled in parallel with the base and emitter circuit of the transistor T1. The cathode of the diode D1 and the emitter of the transistor T1 are connected to the IC ground 16. The IC ground 16 is connected through the IC ground pin 14 to the system ground 10.
Any noise introduced between the IC ground pin 14 and the system ground 10 causes fluctuations on the internal ground bus 16 of the IC. Such fluctuations in the IC ground bus 16 deleteriously effects the ability of the power factor controller to accurately control the power.
For typical power systems, the voltage range is 127 to 380 volts peak or approximately 90 to 270 VAC. The input voltage range to the integrated circuit is about 0.4 to 1.2 volts. Thus, 20 mV of noise in the system ground is a significant portion of the input voltage, i.e. from approximately 5% to 1.6%. A circuit is needed which reduces the effect on the operation a linear IC of noise in the system ground.